According to court documents, 40-year-old Steven Sadler hid his identity using the profile "Nod," and used a fake name to purchase mailboxes at several UPS stores in Washington.

Sadler sent the drugs through the U.S. Mail, where a drug detection dog alerted authorities to an express mail package. Inside, Post Office inspectors found heroin hidden in a birthday card, and scented markers.

Investigators say they used a return address on some of the boxes to track down Sadler, and installed tracking devices on Sadler and his co-defendant's vehicles. During surveillance, the cars traveled to at least 38 Post Offices in the Seattle area.

Court documents show Silk Road sold 1.2 billion dollars worth of drugs and illegal services in about three years.

The Silk Road website protected users with an encryption technique called "onion routing," which is designed to make it "practically impossible to physically locate the computers hosting or accessing websites on the network," court papers said. One listing for heroin promised buyers "all rock, no powder, vacuum sealed and stealth shipping," and had a community forum below where one person commented, "Quality is superb."

"They were comfortable operating in that environment because they felt that they enjoyed complete anonymity," said Jan Fedarcyk, Former Assistant Director with the FBI.

Agents in Seattle eventually connected Silk Road to Sadler after they intercepted a package addressed to someone in Alaska. The recipient told agents where he purchased the drugs from "NOD" on Silk Road.

The FBI recently shutdown the Silk Road website after a two-year undercover operation, and also arrested Ross Ulbricht, the California man who operated the online black market. FBI agents found him in the science fiction section of a small branch of the San Francisco public library, chatting online.

His final mistake, according to the court papers, was ordering fake identification documents from a Silk Road vendor from Canada. One of the nine documents was a California driver's license with Ulbricht's photograph, birthdate but a different name. The package was intercepted at the border during a routine U.S. Customs search.

"Very sophisticated, very intellectual individual who took those skills and talents and developed an online website that marketed illegal goods, illegal services," FBI's Fedarcyk said.

As of July, there were nearly 1 million registered users of the site from the United States, Germany, Russia, Australia and elsewhere around the globe, the court papers said.